diff --git a/src/DefaultPeerStorage.cc b/src/DefaultPeerStorage.cc
index 0f5baa65..b4a9fc00 100644
--- a/src/DefaultPeerStorage.cc
+++ b/src/DefaultPeerStorage.cc
@@ -164,8 +164,24 @@ std::shared_ptr<Peer>
 DefaultPeerStorage::addAndCheckoutPeer(const std::shared_ptr<Peer>& peer,
                                        cuid_t cuid)
 {
+  if (isPeerAlreadyAdded(peer)) {
+    auto it = std::find_if(std::begin(unusedPeers_), std::end(unusedPeers_),
+                           [&peer](const std::shared_ptr<Peer>& p) {
+                             return p->getIPAddress() == peer->getIPAddress() &&
+                                    p->getOrigPort() == peer->getOrigPort();
+                           });
+    if (it == std::end(unusedPeers_)) {
+      // peer is in usedPeers_.
+      return nullptr;
+    }
+
+    unusedPeers_.erase(it);
+  }
+  else {
+    addUniqPeer(peer);
+  }
+
   unusedPeers_.push_front(peer);
-  addUniqPeer(peer);
 
   return checkoutPeer(cuid);
 }
diff --git a/test/DefaultPeerStorageTest.cc b/test/DefaultPeerStorageTest.cc
index ddb870ac..301996f2 100644
--- a/test/DefaultPeerStorageTest.cc
+++ b/test/DefaultPeerStorageTest.cc
@@ -19,6 +19,7 @@ class DefaultPeerStorageTest : public CppUnit::TestFixture {
   CPPUNIT_TEST(testCountAllPeer);
   CPPUNIT_TEST(testDeleteUnusedPeer);
   CPPUNIT_TEST(testAddPeer);
+  CPPUNIT_TEST(testAddAndCheckoutPeer);
   CPPUNIT_TEST(testIsPeerAvailable);
   CPPUNIT_TEST(testCheckoutPeer);
   CPPUNIT_TEST(testReturnPeer);
@@ -42,6 +43,7 @@ public:
   void testCountAllPeer();
   void testDeleteUnusedPeer();
   void testAddPeer();
+  void testAddAndCheckoutPeer();
   void testIsPeerAvailable();
   void testCheckoutPeer();
   void testReturnPeer();
@@ -121,6 +123,38 @@ void DefaultPeerStorageTest::testAddPeer()
   CPPUNIT_ASSERT(!ps.addPeer(peer1));
 }
 
+void DefaultPeerStorageTest::testAddAndCheckoutPeer()
+{
+  DefaultPeerStorage ps;
+  auto btRuntime = std::make_shared<BtRuntime>();
+
+  ps.setBtRuntime(btRuntime);
+
+  auto peer1 = std::make_shared<Peer>("192.168.0.1", 6889);
+  // peer2 and peer3 have the same address and port deliberately.
+  auto peer2 = std::make_shared<Peer>("192.168.0.2", 6889);
+  auto peer3 = std::make_shared<Peer>("192.168.0.2", 6889);
+
+  CPPUNIT_ASSERT(ps.addPeer(peer1));
+  CPPUNIT_ASSERT(ps.addPeer(peer2));
+  CPPUNIT_ASSERT_EQUAL((size_t)2, ps.getUnusedPeers().size());
+
+  auto usedPeer = ps.checkoutPeer(1);
+
+  CPPUNIT_ASSERT_EQUAL((size_t)1, ps.getUnusedPeers().size());
+  CPPUNIT_ASSERT_EQUAL(peer1->getIPAddress(), usedPeer->getIPAddress());
+  // Since peer1 is already used, this fails.
+  CPPUNIT_ASSERT(!ps.addAndCheckoutPeer(peer1, 2));
+  CPPUNIT_ASSERT_EQUAL((size_t)1, ps.getUnusedPeers().size());
+
+  // Since peer2 is not used yet, this succeeds.
+  usedPeer = ps.addAndCheckoutPeer(peer3, 2);
+
+  CPPUNIT_ASSERT_EQUAL((size_t)0, ps.getUnusedPeers().size());
+  CPPUNIT_ASSERT_EQUAL(peer2->getIPAddress(), usedPeer->getIPAddress());
+  CPPUNIT_ASSERT_EQUAL(peer3.get(), usedPeer.get());
+}
+
 void DefaultPeerStorageTest::testIsPeerAvailable()
 {
   DefaultPeerStorage ps;